A filibuster is a type of parliamentary procedure. Specifically, it is the right of an individual to extend debate, allowing a lone member to delay or entirely prevent a vote on a given proposal. It is cynically referred to as talking out a bill,[1] and characterized as a form of obstruction in a legislature or other decision-making body.
The term "filibuster" had been in use for centuries to refer to independent military operators.[2] The term was commonly used in the 1840s for American adventurers who sought to seize power in Central America. The term in its legislative sense was first used in 1854 when opponents tried to delay the Kansas-Nebraska Act in the U.S. Congress.[3]

from Wikipedia

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"From so simple a beginning, endless forms, most beautiful and most wonderful have been, and are being, evolved"

A filibuster only works if you have 40% supporting you so that the rest can not bring cloture (i.e., cut off the filibustering speaker). When a cloture petition is presented, the speaker is literally interrupted on the floor (or at least used to be).

FLOOR STATEMENT OF SENATOR HARRY REID ON REAUTHORIZATION OF THE USA-PATRIOT ACT
“I supported passage of the original PATRIOT Act in 2001, which was enacted in the days immediately following the vicious attacks of September 11, 2001. I do not regret that vote. Much of the original Act consisted of non-controversial efforts to update and strengthen basic law enforcement authorities. More than 90 percent of the 2001 Act is already part of permanent law and will not expire at the end of this year.

“But we are currently considering renewal of those provisions that were considered so expansive and so vulnerable to abuse that Congress wisely decided to subject them to four-year sunsets. The authors of the Act wanted Congress to reassess these authorities in a more deliberative manner with the benefit of experience. Now, more than four years later, we are presented with an opportunity to get it right.

“While the conference report before us makes certain improvements over the original PATRIOT Act, it still does not strike the right balance. We can provide the government with the powers it needs to investigate potential terrorists and terrorist activity and at the same time protect the freedom of innocent Americans. Liberty and security are not contradictory.

“Additional congressional and judicial oversight of the government’s surveillance and investigative authorities need not hamper the government’s ability to fight terrorism. These checks are needed to ensure that the government does not overreach or violate the privacy of ordinary American citizens who have nothing to do with terrorism.

“I am convinced of the need for such checks based in part on information I learned from a Washington Post story that ran in early November, after the Senate had passed its bill. The story reported that the FBI issues more than 30,000 national security letters a year. Chairman Specter says that number is not accurate, but even if half as many letters are issued each year, Congress must act to ensure appropriate protections.